By noon Monday, results from the tests by Mystic Air Quality showed the air was safe from toxic fumes, said Newtown health director Donna McCarthy.

"There was nothing to be concerned about with people occupying the building," McCarthy said, adding the school district consulted with a state toxicologist before allowing people back into the building.

"We had a productive day even though the kids weren't here," Denniston said.

Last Wednesday, area fire department and state environmental officials suspected a leaking underground fuel tank at Reed was causing oil to spill into the Pootatuck River from a nearby stream known as Deep Brook. Officials cleaned more than 50 gallons of oil from the water Wednesday and by Thursday, had stopped most of the oil from reaching the stream.

By Friday, a leaking fuel pump attached to the school's oil tank was tagged the culprit. School officials had switched the building's heating supply to natural gas Wednesday.

On Sunday, Mystic told school officials that air test results would not be finished until Monday, Pitkoff said.

Dropping off his 5-year-old son Connor for speech class shortly after noon Monday, Newtown resident Bill McNerney was surprised to hear the school was closed. Connor comes to the school for 30 minutes every Monday, his dad said.

Richard Ciasullo, the supervising emergency response coordinator with the state Department of Public Health, said more than 3,000 gallons of oil still needed to be located. Ciasullo said the oil likely followed an underground sewer line that leads away from the school toward the brook one-quarter of a mile away. Ciasullo said less than 1,000 gallons of oil was cleaned up by Monday afternoon.

The longer the oil is in the ground, the more likely it could seep into the stream or area ground water, Ciasullo said.